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Main (key) key (word)

mysql PRIMARY KEY constraints syntax

Function: PRIMARY KEY constraint uniquely identifies each record in the database table.

Note: The primary key must contain a unique value. Primary key columns cannot contain NULL values. Every table should have a primary key, and every table can only have one primary key.

mysql PRIMARY KEY constraints example

// 在 "Persons" 表創(chuàng)建時(shí)在 "Id_P" 列創(chuàng)建 PRIMARY KEY 約束
CREATE TABLE Persons(Id_P int NOT NULL,LastName varchar(255) NOT NULL,FirstName varchar(255),Address varchar(255),City varchar(255),PRIMARY KEY (Id_P));